The purpose of this study is to examine the effects of various environmental agents on human peripheral blood leukocytes (HPBL) following in vitro exposures. Three chemical classes of environmental pollutants will be examined, including heavy metals (Pb2+ and Cd2+), polycyclic aromatic hydrocarbons (benzo(a)pyrene), and polychlorinated biphenyls (PCBs). These agents are all immunosuppressive when given to animals or when human cells are exposed in vitro. The overall purpose is to develop biomarkers for immunotoxicity using flow cytometry.